Self-hardening graphite lead for pencils



Patented Nov. 28, 1933 SELF-HARDENING GRAPHITE LEAD FOR ,BENQILS.

Jorgen E. Thomsen, Jersey City, N. J.,assignor to'Joseph Dixon Crucible Company, Jersey City, N. J's-a corporationivewsersey No Drawing. Application-Mariana.193,2

" Seaw- 597 5. I "S-CIaims. 1. 105-5 This invention relates to a self-hardening graphite lead or-marking'ma'terial forpencils and-to the processof making thesame'.** One of the objectsof this invention is to prov 1 vide a selfehardeningi graphite lead-which; ;by reason of its characteristics,may be made into coils .orrolls of I any-desired lengths, enabling various novel methods .of pencil manufacture-to be employed which are impractical where the ordinary hardenedlead in relatively short=lengths is used. A further object of the invention-is to avoid the warping and breakagewhich frequently occurs with the ordinary hardened graphite lead.- f -15 Graphite lead aszmanufactured at the present time consistspf a combination of graphite, clay and wax. Thengraphite and clay are mixed in varied proportions according to the degree of hardness required in the lead and this mixture 0 isthen formed into relatively shortlengths which aredried and later calcinedto'liarden the mixture. After thecalcining operation, the leads arewaxedtoimproveitheir writing qualities, and are then readyfor insertion in the pencil sheaths. The drying and heating operations-employed in the conventional process iofimakin'g hardened graphite -leadsxoften causes warping of "the leads which either break when an attempt is-madeto insert them in a pencil sheath, 'or else are so badly warped as to render them unfit for-use. Consequently; the manufacture'of the ordinary hardened graphite lead involves considerable waste. 1 v f 1 This invention comprehends the production of a self-hardening graphite lead, some-"of'the ad-' vantages of which are these: Such a lead or marking material may be of i great length" (that isyof: indefinitely greater length'than' the usual hardened lead); it may be convenientlymam; tained-inicoiled or rolled condition for a reason:

able period of time until ready for use, and'in combination with a plastic sheath or covering it may be employed to form pencils speedily and inexpensively. The warping and breakage so 5 characteristic of the ordinary or hardened graphite lead is avoided with resultant saving in the cost of manufacture of the pencils.

There are several ways in which a self-hardening graphite lead or marking material may be made in accordance with this invention. One

method involves the mixing and grinding together of clay, graphite and water, with or without the addition of such carbonaceous substances as lamp black or pyrographitic acid; the drying of the ground mixure in small masses or lumps;

theburning or heating of these dried lumps; the impregnation of the. clay, graphite and-carbonaceous substance (if used) by wax; the grinding of the-lumps intov a powdered massandtheimixing of. the powder. with suitable:ingredientsto 5p forma plastic mass which isldried to the desired plasticity and extruded into a round, flexible rod ofrindefinite length-1 '1 In carrying outthe process; thus. briefly ,de-' scribed, --stockis prepared .by-;grinding awmass 6d composed'of a mixture of water graphiterand clay, to which the carbonaceoussubstancesuch as lamp black 'or-pyrographitic acid may ibeadded if a :veryblack'lead isrequired. .-The :mass so formed is thendivided into smaller portions '(0; or lumps to facilitate drying, thedrying being performed .by exposing the lumps" to the action of .air, or. by any. of f the other drying-processes common .toithis art. When dried, the'lumpstare heated or calcined, which-greatly adds-.toitheir [Q porosity. .These' calcined'lumps are; then "immer'sed in moltenwaxafor 'avperiodtof time suificientijto cause the wax to penetrate, the pores ofthe mixture and-surround and adhere to-the graphite particles" therein. and to the particles so, of the carbonaceous" substance, if used. :Six,.-.0r seven hours-is usually sufiicientto cause ,a thor. ough penetration of the wax into the 'poreszof the mixture and a coating of.-thez.graphit'e--and carbonaceous substance: particles byithewax. The lumps now' composed of ,a' mixture of .calcined clay, graphite and possibly the carbona' ceousmaterialand wax :are then reduced-to fa powderby grinding. The ground or: powderedmass'is'then' mixediwith awa'ter soluble organic 9Q compoundwhich servesi'as a binder, or-a-bond ing element. I have found a water-.solublecel lulose' compound, such as an alkyl derivative of cellulose, "very satisfactory for the purpose? Thesealkyl-cellulose compounds 'are at the'pr'es .5., ent time, available in the open market and are water-soluble binding agents advantageously used in my composition- They may be prepared, for instance, in the manner described in the patents to Lilienfeld Nos. 1,188,376 and 1,505,043 199 and numerous others. However, it is more convenient to purchase the alkyl cellulose binding agent from a manufacturer thereof. When employed as herein set forth three to twenty per cent by volume is used in the mixture. The more alkyl cellulose binder employed the harder will be the mixture. Instead of alkyl cellulose binder, gum tragacanth may be employed in the same proportions, although its use is not'particularly ll!) (if used), calcined clay, wax, alkyl cellulose binder, bentonite and water. This mass is dried in any suitable way, such as by passing it through a screen which acts to break the mass up and facilitate drying it. By making suitable tests during the drying operation it can be easily ascertained when the mixture is in its proper condition for extrusion to form the lead. Tests indicate that the mass is satisfactory for extrusion when it contains approximately twelve to twenty per cent water. When the drying has progressed to the required extent, the extrusion is performed which converts the mass into a lengthy, flexible, rod-like section of lead. Since it is soft, the lead section can be formed into a roll or coil and can'be kept from hardening for a reasonable period of time, such as from two to three weeks by storing it in an airtight container.

' Another satisfactory method of making the improved self-hardening graphite lead is substantially as follows:

Graphite is ground to the proper degree of fineness in water. To this graphite and water mixture is added chlorinated naphthalene and a wax. Since the chlorinated naphthalene is later removed from the mixture by distillation the amount employed is relatively unimportant. The amount of wax employed is from five to ten per cent by volume of graphite. I

The mixture, consisting of graphite, chlorinated naphthalene and wax is agitated, the chlorinated naphthalene cleaning and purifying the graphite so as to cause the wax to intimately coat or adhere to the graphite particles.

' Instead of using chlorinated naphthalene in the mixture, it is entirely feasible to use a volatile oil mixing it with wax and a benzol compound, such as xylol, with satisfactory results.

When the mixture has been prepared the water therein, containing the impurities cleansed from the graphite by the action of the chlorinated naphthalene, is removed by decantation and then the chlorinated naphthalene (or oil and xylol, if used) is removed by distillation. This leaves v a powdered mixture of wax-coated graphite to which may be added, if desired, a carbonaceous material, such as lamp black or pyrographitic acid, in such quantity as necessary to produce a lead of required blackness. This mixture is then mixed with alkyl cellulose binder, bentonite and water, as previously described in connection with the first method of carrying out this invention. The resultant mass is dried to the required extent and is extruded to form it into a soft, self-hardening lead in the form of a continuous flexible rod 'of indefinite length which will retain its flexibility, when kept in an airtight container, for several weeks. Such lead, since sheathed while soft, 35 does not crack or break and consequently losses from waste are small. This. self-hardening lead can behandled in very lengthy form since it can be conveniently rolled or coiled, and it enables pencils, and particularly those which have a sheath composed of a plastic material, to be made by an extrusion method not possible when hard, short-length leads are used.

What I claim is:-

1. A marking material for pencils containing a comminuted wax-saturated calcined graphite and a water-soluble binder.

2. A self-hardening lead materialv for pencils containing a comminuted wax-saturated calcined graphite, and-a binder composed of a water-- 1 soluble cellulose material.

3. A self-hardeninglead comprising graphite and clay, calcined together, wax-saturated and comminuted, a water-soluble organic compound forming a binder and an inorganic 'plasticizing 5 agent.

i. A self-hardening lead comprising a comminuted mixture of calcined and Wax-saturated graphite and clay, a water-soluble cellulose material, a plasticizing agent and water. n

5. A self-hardening lead comprising a comminuted mixture of calcined and Wax-saturated graphite and clay, alkyl cellulose, bentonite and water.

6. A self-hardening lead comprising com- 1 minuted wax-coated calcined graphite, a watersoluble binder and a' plasticizing agent.

7. The method of making a self-hardening' graphite lead consisting in calcining a' mixture containing clay and graphite, in impregnating the mixture with wax, in reducing the wax-impregnated mixture to powder form, in mixing a water-soluble binder with the powder mass, in adding a plasticizing agent thereto, in drying the mixture and forming it into lengths. 25 

